The invention generally relates to electrode structures deployed in interior regions of the body. In a more specific sense, the invention relates to electrode structures deployable into the heart for diagnosis and treatment of cardiac conditions.
The treatment of cardiac arrhythmias requires electrodes capable of creating tissue lesions having a diversity of different geometries and characteristics, depending upon the particular physiology of the arrhythmia to be treated.
For example, a conventional 8 F diameter/4 mm long cardiac ablation electrode can transmit radio frequency energy to create lesions in myocardial tissue with a depth of about 0.5 cm and a width of about 10 mm, with a lesion volume of up to 0.2 cm3. These small and shallow lesions are desired in the sinus node for sinus node modifications, or along the A-V groove for various accessory pathway ablations, or along the slow zone of the tricuspid isthmus for atrial flutter (AFL) or AV node slow pathways ablations.
However, the elimination of ventricular tachycardia (VT) substrates is thought to require significantly larger and deeper lesions, with a penetration depth greater than 1.5 cm, a width of more than 2.0 cm, with a lesion volume of at least 1 cm3.
There also remains the need to create lesions having relatively large surface areas with shallow depths.
One proposed solution to the creation of diverse lesion characteristics is to use different forms of ablation energy. However, technologies surrounding microwave, laser, ultrasound, and chemical ablation are largely unproven for this purpose.
The use of active cooling in association with the transmission of DC or radio frequency ablation energy is known to force the electrode-tissue interface to lower temperature values, As a result, the hottest tissue temperature region is shifted deeper into the tissue, which, in turn, shifts the boundary of the tissue rendered nonviable by ablation deeper into the tissue. An electrode that is actively cooled can be used to transmit more ablation energy into the tissue, compared to the same electrode that is not actively cooled. However, control of active cooling is required to keep maximum tissue temperatures safely below about 100xc2x0 C., at which tissue desiccation or tissue boiling is known to occur.
Another proposed solution to the creation of larger lesions, either in surface area and/or depth, is the use of substantially larger electrodes than those commercially available. Yet, larger electrodes themselves pose problems of size and maneuverability, which weigh against a safe and easy introduction of large electrodes through a vein or artery into the heart.
A need exists for multi-purpose cardiac ablation electrodes that can selectively create lesions of different geometries and characteristics. Multi-purpose electrodes would possess the requisite flexibility and maneuverability permitting safe and easy introduction into the heart. Once deployed inside the heart, these electrodes would possess the capability to emit energy sufficient to create, in a controlled fashion, either large and deep lesions, or small and shallow lesions, or large and shallow lesions, depending upon the therapy required.
The invention provides electrode structures formed from flexible, porous, or woven materials, and associated methods for forming them.
One aspect of the invention provides a formed electrode structure made by separately forming first and second body sections, each including a peripheral edge. The first and second body sections are joined together about their peripheral edges with a seam, thereby forming a composite structure.
In a preferred embodiment, at least one functional element is enveloped within the seam as the seam is formed.
In a preferred embodiment, at least one of the materials is porous or woven. However, this aspect of the invention is applicable for use with any flexible material in general.
According to this aspect of the invention, the seam is formed by thermal bonding, ultrasonic welding, laser welding, adhesive bonding, or sewing the peripheral edges together.
In a preferred embodiment, the composite body is everted to locate the seam inside the composite structure.
Another aspect of the invention provides an electrode structure made by forming a body having a three dimensional shape and opposite open ends, and at least partially closing at least one of the opposite ends by forming a seam. According to this aspect of the invention, the body is preferably porous or woven, although flexible materials in general can be used. The seam is formed by thermal bonding, or ultrasonic welding, or laser welding, or adhesive bonding, or sewing. In a preferred embodiment, the body is everted to locate the seam inside the body. Also in a preferred embodiment, at least one functional element is enveloped within the seam as the seam is formed.
Another aspect of the invention provides an electrode structure formed from a sheet of porous, or woven, or flexible material having peripheral edges. The sheet is placed on the distal end of a fixture, while the peripheral edges of the sheet are gathered about the proximal end of a fixture, thereby imparting to the sheet a desired shape. According to this aspect of the invention, at least one pleat is formed to secure the gathered peripheral edges together. The pleat is formed by thermal bonding, or ultrasonic welding, or laser welding, or adhesive bonding, or sewing.
Other features and advantages of the inventions are set forth in the following Description and Drawings.